Silicon and SunKevin Bullis, MIT Technology Review In his lab facing the Pacific Ocean, Daniel Morse is learning new ways to build complex semiconductor devices for cheaper, more efficient solar cells. He has an unlikely teacher: sea sponges. ---- In his beachfront office overlooking the Santa Barbara channel, Daniel Morse carefully unwraps one of his prized specimens. An intricate latticework of gleaming glass fibers, it looks like a piece of abstract art or a detailed architectural model of a skyscraper. But it's actually the skeleton of one of the most primitive multicellular organisms still in existence--a species of marine sponge commonly known as Venus's flower basket. Morse, a molecu­lar biologist at the University of California, Santa Barbara, wants to know how such a simple creature can assemble such a complicated structure. And then he wants to put that knowledge to work, making exotic structures of his own.

The lowly sponge has come up with a remarkable solution to a problem that has puzzled the world's top chemists and materials scientists for decades: how to get simple inorganic materials, such as silicon, to assemble themselves into complex nano- and microstructures. Currently, making a microscale device--say, a transistor for a microchip--means physically carving it out of a slab of silicon; it is an expensive and demanding process. But nature has much simpler ways to make equally complex microstructures using nothing but chemistry--mixing together compounds in just the right combination. The sponge's method is particularly elegant. Sitting on the seabed thousands of meters below the surface of the western Pacific, the sponge extracts silicic acid from the surrounding seawater. It converts the acid into silicon dioxide--silica--which, in a remarkable feat of biological engineering, it then assembles into a precise, three-dimensional structure that is reproduced in exact detail by every member of its species.

What makes the sponges' accomplishment so impressive, says Morse, is that it doesn't require the toxic chemicals and high temperatures necessary for human manufacture of complex inorganic structures. The sponge, he says, can assemble intricate structures far more efficiently than engineers working with the same semiconductor materials.

This primitive creature and a number of other marine organisms have become an inspiration for researchers who hope to find simpler and cheaper ways to build inorganic structures, such as semiconductor devices, for use in computer microchips, advanced materials, and solar cells. (8 Nov 2006)

Cheap, Superefficient SolarKevin Bullis, MIT Technology Review Solar-power modules that concentrate the power of the sun are becoming more viable. ----- Technologies collectively known as concentrating photovoltaics are starting to enjoy their day in the sun, thanks to advances in solar cells, which absorb light and convert it into electricity, and the mirror- or lens-based concentrator systems that focus light on them. The technology could soon make solar power as cheap as electricity from the grid.

The idea of concentrating sunlight to reduce the size of solar cells--and therefore to cut costs--has been around for decades. But interest in the technology has picked up in the past year. Last month, Japanese electronics giant Sharp Corporation showed off its new system for focusing sunlight with a fresnel lens (like the one used in lighthouses) onto superefficient solar cells, which are about twice as efficient as conventional silicon cells. Other companies, such as SolFocus, based in Palo Alto, CA, and Energy Innovations, based in Pasadena, CA, are rolling out new concentrators. And the company that supplied the long-lived photovoltaic cells for the Mars rovers, Boeing subsidiary Spectrolab, based in Sylmar, CA, is supplying more than a million cells for concentrator projects, including one in Australia that will generate enough power for 3,500 homes.

The thinking behind concentrated solar power is simple. Because energy from the sun, although abundant, is diffuse, generating one gigawatt of power (the size of a typical utility-scale plant) using traditional photovoltaics requires a four-square-mile area of silicon, says Jerry Olson, a research scientist at the National Renewable Energy Laboratory, in Golden, CO. A concentrator system, he says, would replace most of the silicon with plastic or glass lenses or metal reflectors, requiring only as much semiconductor material as it would take to cover an area the size of a typical backyard. And because decreasing the amount of semiconductor needed makes it affordable to use much more efficient types of solar cells, the total footprint of the plant, including the reflectors or lenses, would be only two to two-and-a-half square miles. (9 Nov 2006)

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